Some of these compounds are already known, there may be mentioned, in particular, compound (Ia): ##STR3## which is a synthesis intermediate for anticancer substances which are described in French Patent Application No. 2,436,786, and which is obtained by a complex method, since it comprises twelve stages, starting from: ##STR4##
There may also be mentioned compound (Ib): ##STR5## which is a synthesis intermediate for anticancer substances which are described in French Patent Application No. 2,387,229, and which is obtained in a low yield by an eleven-stage method starting from the compound: